This is a two battery power bank from Soshine with a nice display.
Official specifications:

Capacity: 5200 mah

Battery Type: Lithium Ion

Input: DC 5 v / 1 - 2.1 - 6 v 5 w (solar panel)

Output: DC 5 v / 1 / 2.1 (adjustable)

Input: USB-micro B type

Operating temperature: 0 ~ 40

Energy storage battery: lithium 2600 mah

Charging time: USB-micro B-type: input Approx. 2000mAH: 3 - 4 hours

Color: white

Size (cm): L 11.5 x H 2.7 x W 4.7 cm / 4.53 x 1.06 x 1.85 in

Weight (without battery) 160 g, 298 g (with packaging)

I got it from Aliexpress dealer: Top one 3C Store
The specifications are a bit misleading, the box is supplied without battery and any 18650 can fit, including 3600mAh.

How does it look

The power bank is delivered in a cardboard box with a window at the front and some specification on the back.

It included the power bank, a usb cable and a instruction sheet

The power on button is placed on the bottom of the box.

To replace the batteries the lid can be slided to the display side, but it cannot be removed.

The white strip makes it easier to get the batteries out.

There is space for two batteries from 61mm to about 69mm, this means button top and some protected cells can be used.

When batteries are put in or the on button is pressed the power bank turns on and the display will show battery status, output voltage, usb current drain, on time.

When connected to charge voltage the display will show battery voltage (More or less), battery status, charged capacity and time.

Measurements

Device can work as ups, but output voltage can be a bit low (4.5V).

Battery charging will resume silent if the voltage drops

Charging will resume if input voltage cycles or battery is removed/inserted.

When battery is full the charger will charge with 2mA when powered

The battery is discharged with about 4mA when not powered (This is rather high for a power bank).

USB out is with automatic coding: DCP, Samsung, Apple2.1A

USB output turns off after about 30 seconds with less then 25mA load.

Display, background light and electronic uses about 35mA from batteries when on.

Voltmeter will show battery voltage when charging and usb voltage when not charging.

Voltmeter will not reduce reading, but always show maximum value (Up to 4.2V).

Voltmeter is not very precise.

Size: 113.1 x 47.7 x 27mm

Weight: 62g (Batteries not included)

One full battery can deliver about 2.2A before the output drops. The voltage will be on the low side at high current.

The other slot can deliver the same.

With two batteries the output can reach 2.5A

If input power is supplied with batteries in the box the output voltage is fairly low.

Without batteries the output voltage starts at 5V, but drops fairly fast.

The display will show the usb output current.

The box has stable output voltage at 0.5A, but the voltage is a bit low. The discharge stops at around 2.8V

It is the same with the other battery.

Two batteries give a bit more than double time.

At 1A the output voltage is dropped a bit more, everything looks fine.

Drawing 2A with one battery is outside the specifications, but it can do it for a short time.

It works much better with two batteries, but the voltage is around minimum usb voltage.

Here I slowly reducing the battery voltage (Takes about 20 minutes) while I measure the current draw. This shows the standby power consumption.

The noise at 0.5A is 14mV rms and 108mVpp

The noise at 1A is 13mV rms and 138mVpp

The noise at 2A is 24mV rms and 161mVpp, all values are very low.

The charging is a good CC/CV profile with a low termination current of about 50mA. The maximum charger current is about 2A.

This battery was rather discharged and the charger used a low current until the battery reached 3.1V (good)

With two batteries in the box the charge current drops to 1A. The input current from usb is still around 1.6A

Conclusion

This power bank and charger has a nice display with a lot of information, the charging is good, but current is on the high side for some batteries. The usb output is good with low noise, but I would have like a bit higher voltage when loaded. It has some flexibility with battery length.
I have one problem with it, that is the discharge rate when not used, with this discharge rate it is best not to keep batteries in it for longer time. It is fine enough for a week or two, but do not if there is months between charging.